1. Field of the Invention
The present invention relates to an apparatus and a method for video signal processing, and a camera device and a method therefor, using the apparatus and method for video signal processing. In particular, the invention relates to the apparatus and method for video signal processing for correcting a contour of a picture, and the camera device and method therefor, using the apparatus and method for video signal processing.
2. Description of Related Art
There is known a method for increasing the resolution of a picture, e.g., disclosed in JP-A Nos. 38074/1983 or 29578/1991. The method has, with regard to a camera device, a step of generating a contour correction signal consisting of a preshoot and an overshoot in a horizontal or vertical direction from a video signal for correcting the deterioration of a frequency characteristic through an aperture of an image pickup device, and a step of adding this contour correction signal to the original video signal thereby to increase the resolution of a picture.
FIG. 2 is a block diagram showing one conventional example of a contour correction circuit used in a video signal processing apparatus. Numeral 1 is a contour correction circuit, 1a is a contour correction signal generation unit, 1b is a gain adjustment unit, 1c is an addition unit, 1d is an input terminal, and 1e is an output terminal.
FIG. 3 is a waveform chart showing a signal of each unit in FIG. 2, and the signal that corresponds to FIG. 2 is marked with the same symbol.
In FIGS. 2 and 3, a digital video signal a input from the input terminal 1d is supplied to the addition unit 1c and the contour correction signal generation unit 1a in the contour correction circuit 1. At this point, FIG. 3(a) shows a portion (a leading or trailing edge portion) in which the contour of this digital video signal a exists.
In the contour correction signal generation unit 1a, a high frequency component of this digital video signal a is sampled. A contour correction signal b consisting of the preshoot and overshoot shown in FIG. 3(b) that synchronize with a contour portion of the digital video signal a is generated from this high frequency component. This contour correction signal b is supplied to the addition unit 1c after a gain has been adjusted by the gain adjustment unit 1b, and is added to the original digital video signal a input from the input terminal 1d. Accordingly, the output terminal 1e obtains a digital video signal c in which the contour portion was enhanced and corrected by undershooting on the low luminance level side and overshooting on the high luminance level side in the contour portion of the original digital video signal a.
According to such contour correction processing, in a conventional digital video signal processing apparatus that primarily handles a moving picture, there was an effect indicating that a feeling for the resolution of a picture increases and image quality improves.
Incidentally, the object of contour correction is to increase an inclination of an edge, but it is not ideal that an undershoot and an overshoot are generated. Accordingly, an art of reducing these undershoot and overshoot is proposed (refer to JP-A No. 316393/1993).
This art indicates that when a contour correction signal including an undershoot and an overshoot is generated in the same manner as described above, the time width of these undershoot and overshoot is shortened by passing this signal through a switching means, and, subsequently, the contour correction signal processed in this manner is added to the original video signal.
Moreover, the invention relates to an interpolation device and method for sample interpolation used in the enlargement of a digital picture, and, more particularly, to a camera device and its imaging method.
An interval (cycle) of a sample (pixel) is also enlarged to sample a part of a digital picture, and to enlarge and display this part. Accordingly, inter-sample interpolation is performed to match the original sample cycle. As such an interpolation method of a conventional image, a linear interpolation method is cited (for example, refer to “More Plain Digital Video Processing” 9th Edition, Published by Hitoshi Kitsuka, CQ Publishing Company, on Aug. 1, 2003, on pp. 168 to 174).
The conventional interpolation method will be described using FIG. 12.
Now, a picture is cut out in a certain direction (for example, a horizontal scanning direction), and a picture P1 having an edge between samples A and B is targeted, as shown in FIG. 12(a), regarding a unit in which the vertical axis indicates a signal level or the horizontal axis indicates a sample cycle t as distance.
When an area including this edge of a part of this type of picture P1 is sampled and this area is enlarged into four times, this edge portion becomes a picture P2 shown in FIG. 12(b). At this point, this picture P2 has the sample cycle T=4t and turns into a very coarse picture. At this point, the samples A, B are the samples A, B in FIG. 12(a). The signal level of the sample B changes greatly for the sample A because of the aforementioned edge.
Further, this type of picture P2 corresponds to a picture as well in which a sample was sampled in the cycle T.
A sample is interpolated to improve the image quality of this type of coarse picture P2. Linear interpolation is performed hitherto as this type of interpolation method, but FIG. 12(c) shows a picture P3 in which this type of linear interpolation was performed. This linear interpolation method connects adjacent samples by a straight line and interpolates the sample of the signal level on this straight line in a cycle t.
In this type of linear interpolation method, a sample at adjacent two points is filtered. Moreover, according to a filter using information about an unlimited sample on a time axis that extends endlessly, as shown in FIG. 12(d), the sample can be interpolated at a point on a sine wave of the, cycle 2T connecting the samples A and B based on a sampling theorem. In reality, interpolation data approximate to the interpolation shown in FIG. 12(d) can be obtained by using a filter having a characteristic approximate to an ideal using the limited number of samples. As the method in which the filter of the characteristic approximate to the ideal using such limited number of samples was used, there is a bicubic method (for example, refer to JP-A No. 2001-157217).